Secularism provides no guarantees that humans in power will always do what is right or good but neither does religion.Soviet Russia, Vietnam, Cambodia? These were all religious nations?
As far as I know, Adolf Hilter and other tyrants throughout history did not believe in faeries. Should we assume that leaders who do not believe in faeries are more likely to commit crimes against humanity than leaders who do believe in them?But this is about atheism. Atheists are the mass murderers and genocide purveyors throughout history, not Christians.
Try to keep in mind that if the Book of Genesis is true then God is the greatest mass murderer of all time... men, women, and children... all collectively punished for the sins of the wicked.